Linked: How everything is connected to everything else and what it means for business, science, and everyday life

June-6-2017

Chapter 9-1: Achilles's heel

对于小世界网络，网络之所以具有高通性和高的传播效率，是因为网络中存在一些“hubs枢纽”节点，它们将网络中的大小节点紧密联系在一起，使得信息和能量能在网络中快速传播。然而，在随机攻击（randomly select a node to attack)或蓄意攻击（target hubs)下，节点会失效。因此，小世界网络虽然有高连通性，但同时也具有脆弱性。

Due to the hignly interconnected relationship of a small-world network, the failure in a few hubs can lead to failure in other nodes, and even destory the whole network.

The distinguishing feature of scale-free networks is the existence of hubs. the few highly connected nodes that keep these networks together. Failures (e.g., due to random attack), however, do not distinguish between nodes but affect small nodes and large hubs with the same probability.

Node failures can easily break a network into isolated, noncommunicating fragments. Such fragmentation is a well-known property of networks affected by failures.

Clearly, the more nodes we remove from a network, the more likely we wold isolate large chunks of nodes.

Small nodes contribute little to a network's integrity, thus the removal of small nodes may not destroy a system into isolated parts.

Most node attacks are not randomly selected, but targeting the hubs.

Although scale-free networks are vulnerable to attack, several of the largest hubs must be simultaneously removed to crush them.

Chapter 9-2: Cascading failure

When a network acts as a transportation system or a power system, a local failure shifts load or responsibilities to other nodes. If the extra load is negligible, it can be seamlessly absorbed by the rest of the system, and the failure remains effectively unnoticed. If the extra load is too much for the neighboring nodes to carry, they will either tip or again redistribute the node to their neighbors. Either way, we are faced with a cascading event, the magnitude and reach of which depend on the centrality and capacity of the nodes that have been removed in the first round.